Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,821   Posts: 1,581,701   Online: 981
      
Page 3 of 5 FirstFirst 12345 LastLast
Results 21 to 30 of 49
  1. #21

    Join Date
    Nov 2004
    Location
    Italia
    Shooter
    Multi Format
    Posts
    4,680
    [QUOTE=cao] The spec sheets for the Luxeons seem to require a constant current somewhere between 750ma and 1000ma for operation. /QUOTE]


    My understanding is 750 you get the stated light output and lifespan. 1000 you get more light but less life. OTOH I'm not sure the lower lifespan would really matter in an enlarger. But if you use less then 750 you'll get less light but longer life?

  2. #22
    Jon King's Avatar
    Join Date
    Sep 2002
    Location
    New Hampshire
    Shooter
    Medium Format
    Posts
    360
    Images
    14
    Nick - The 5W LEDs are expensive, but cheaper per lumen. That's one reason I am looking at using a mixing chamber vs the approach Huw took. Even higher output LEDs are on the way - one goal of companies like Luxeon is to replace car headlights with a single LED. For my final version, I have a PWM ckt designed (a bit too much like real work - designing analog power converter ICs pays for my photographic efforts ) that will get the voltages and currents where they need to be, as well as dimming.

    cao- it would be very interesting to find out what that frequency is. A problem with low cost digital solutions for pulsing circuits is that they are pretty slow. Analog controllers are actually superior in that aspect, as if most of us on APUG don't realize that already


    Jon

  3. #23
    cao
    cao is offline
    cao's Avatar
    Join Date
    Oct 2004
    Shooter
    35mm
    Posts
    188
    Quote Originally Posted by jking
    cao- it would be very interesting to find out what that frequency is. A problem with low cost digital solutions for pulsing circuits is that they are pretty slow.
    Jon
    There's also a limit on how fast we can switch the Luxeons as I seem to recall; the optical rise is about 10ns, and I have no idea what sort of shape that is. So let's say, we won't modulate above 2MHz. Still, you need fairly fast power FETs and the smarts to drive them. I have a number of ideas here, but capitalizing them is another thing altogether, and again for what sized market? Many folk seem happy enough with incandescent bulbs and plastic filters.

  4. #24

    Join Date
    Nov 2004
    Location
    Italia
    Shooter
    Multi Format
    Posts
    4,680
    The problem for me is the cost seems too high still. 30 LEDs end up costing $450 at $15 per III model LED. Plus all the other parts of the head. The upside is it looks like the LEDs would last almost forever in enlarger use. No bulb replacement costs. I know I'm not the only one that would like a bigger enlarger for light usage. The ones out there are either huge. Expensive. Or have other issues. I think I'll have to wait for LED costs to come down some more.

  5. #25
    eheldreth's Avatar
    Join Date
    Aug 2004
    Location
    West Virginia
    Shooter
    Multi Format
    Posts
    113
    Images
    2
    Thanks for all the replies, I think the information on Huws home page is a great place to start. This should keep me busy enough this winter.

  6. #26

    Join Date
    Jun 2003
    Shooter
    Medium Format
    Posts
    18
    I tried some brief experiments with some green and blue LED's desgined for instrment displays. The one thing that really surprised me is that the VC paper was nearly unresponsive to the green LED. Even making a tiny print, though a very thin negative took a very long time. In fact the paper was so insensitive to the green LED's it made me wonder if they would make a good safe light (I currently use red LED's for a safe light).

    I notied that the color of the big bright 1W and 5W green LED that Huws used was different than the ones I was experimenting with (peak emission frequency was different). I suspect that this makes all the difference in the world.

    The blue LED's required very short exposures .. but only got me to about grade 4.

    Ken

  7. #27
    rjr
    rjr is offline
    rjr's Avatar
    Join Date
    Aug 2004
    Location
    Mosel, SW Germany
    Shooter
    Medium Format
    Posts
    409
    Images
    4
    Jon,

    "I'll happily share the schematic if anyone wants to experiment with the LEDs. If you can solder, you can build this pretty easily."

    Yes, please! Me being an electronic dummy, but having a friend who already built a few LED darkroom lamps for me... perhaps I can pursue him to solder a head for my Durst Duomat in exchange for your schematics. ;-)
    Tschüss,
    Roman

  8. #28

    Join Date
    Sep 2004
    Location
    Netherlands
    Shooter
    Medium Format
    Posts
    1,336
    On the Photokina 2004 in Köln I saw the prototype of Heiland's split grade cold light unit, build over with high intensity LED's. Green, blue and red. Green and blue for the split grade exposures, red for an overall view of the negative, I think. It was a new development, planned for 2005.

  9. #29
    Jon King's Avatar
    Join Date
    Sep 2002
    Location
    New Hampshire
    Shooter
    Medium Format
    Posts
    360
    Images
    14
    Quote Originally Posted by rjr
    Jon,

    "I'll happily share the schematic if anyone wants to experiment with the LEDs. If you can solder, you can build this pretty easily."

    Yes, please! Me being an electronic dummy, but having a friend who already built a few LED darkroom lamps for me... perhaps I can pursue him to solder a head for my Durst Duomat in exchange for your schematics. ;-)
    Sorry for the delay, but the holidays have gotten in the way

    I attached a jpg of the schematic as well as a snapshot of my initial light source. This can be easily adapted to digital control if desired. I'm going to use this one to build the mixing box, then adjust the number and power of LED's to get the light output where it needs to be for reasonable printing times, and a more power efficient source - all work to do...


    A quick note or two. for M1 I used an IRLIZ14G, but any MOSFET with the proper voltage and current rating should work. Your friend should not have much problem finding something suitable. It will get hot - a good heat sink is necessary. The LEDs also need one. Their light output drops as their temperture increases, so for consistant light output during a printing session, a heat sink is needed here too.

    Hope this helps,
    Attached Thumbnails Attached Thumbnails lumiled_source_small.jpg   LED Enlarger Lit.jpg  
    Jonathan
    -----------------------------------------------

  10. #30
    Jim Moore's Avatar
    Join Date
    Oct 2003
    Location
    Iowa
    Shooter
    Large Format
    Posts
    885
    Images
    16
    Just wondering how those of you who are building an LED light head are coming along with your projects...

    I'm thinking of doing one of these for my 8x10.

    Jim
    "You miss 100% of the shots you don't take"...Wayne Gretzky

Page 3 of 5 FirstFirst 12345 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin